Method of chemical treatment and chemically treated member

ABSTRACT

A chemical treatment method in which an object to be treated is treated with a chemical treating agent to form a chemical conversion coating, in which the object to be treated has at least one aluminum-plated steel sheet and at least one member selected from the group consisting of cold-rolled steel sheets, zinc-plated steel sheets, and aluminum sheets and the chemical treating agent is one which has zirconium, fluorine, and an aminated silane coupling agent and in which the zirconium content is 100-700 ppm in terms of metal amount and the fluorine/zirconium ratio is 3.5-7.0 by mole. A sufficient coating amount can be ensured on the surface of a zinc deposit, cold-rolled steel sheet, zinc-plated steel sheet, aluminum-plated steel sheet, or the like and a chemical conversion coating having sufficient base-hiding properties and sufficient adhesion can be formed.

TECHNICAL FIELD

The present invention relates to a method of a chemical conversiontreatment, and more specifically, relates to a method of a chemicalconversion treatment suited for pretreatment prior to painting ofgeneral industrial products, particularly automotive bodies, and amember subjected to a chemical conversion treatment obtained by themethod of the chemical conversion treatment.

BACKGROUND ART

Conventionally, automotive bodies are configured with bases of softsteel plates such as unprocessed iron materials and galvanized steelplate, and aluminum and the like. Exemplary surface treatment techniquefor these items includes treatment with zinc phosphate, in which a zincphosphate coating film is deposited on a material surface, therebyensuring the corrosion resistance and adhesiveness of the painting.(See, Patent Document 1).

However, recently a broad range of materials have been used forautomotive bodies in order to achieve lower weight bodies. Inparticular, the application of high-tensile steel plates has beenrapidly increasing. Desired characteristics for steel plates such asstrength, elongation and the like vary depending on which part of theautomotive body they are applied. For example, with respect to strength,there are a variety of classes, i.e., from 270 MPa class to 1500 MPaclass or greater. Among these, steel plates having strength of 440 MPaor greater are referred to as high-tensile steel plates, while thosehaving strength of less than 440 MPa are referred to as soft steelplates, in general.

With such a broad range of steel plates, steel plate alloy compositionand production methods varies depending on the required characteristics.Particularly, as the amount of Si component increases, etchability ofthe material surface deteriorates, leading to non-uniformity of thedeposition of the zinc phosphate coating film when treated with aconventional zinc phosphate coating technique. Thus, it is not easy toensure the corrosion resistance and adhesiveness of the coated film.Furthermore, in ultra high-tensile steel plates having a strengthexceeding 1000 MPa, accuracy of the size attained in forming is inferioraccording to common cold stamping production methods. Therefore, hothardening such as induction hardening is carried out after theformation, or a hot stamping production method is employed in whichheating is conducted during forming. Thus, it becomes more difficult toensure the adhesiveness and corrosion resistance of the coated film.Particularly, in hot stamping production methods, the material surfaceis oxidized by thermal history when the unprocessed iron material isused, thereby failing to achieve the corrosion resistance andadhesiveness of the coated film. In order to achieve satisfactorycorrosion resistance and adhesiveness, elimination of the oxide scale byshot blasting is a prerequisite, thus leading to economicaldisadvantages. Hence, as a procedure for preventing surface oxidation inhot stamping, aluminum coated steel plates have been extensively used.

According to a feature of the aluminum coated steel plates, heatingduring formation results in diffusion of the coated component on theiron basis metal, whereby the AlFe alloy is produced. Since this AlFealloy is stable, high corrosion resistance is exhibited. In contrast,because no common zinc phosphate coating film is formed what so ever,sufficient adhesiveness of the coated film cannot be achieved. This isbased on resistance to etching because of the stability irrespective ofthe requirement of continuous electron donation by etching of thematerial for deposition of the crystalline zinc phosphate coating film.

Accordingly, a novel surface treatment technique for deposition of anamorphous coating film has been desired which enables a metal product tobe coated by electron donation with slight etching of the material. Forexample, a surface treatment technique based on a zircon coating film isexemplified, which was proposed also as a surface treatment method ofautomotive bodies (see, Patent Document 2). Moreover, in light ofenvironmental protection, and discharge of sludge being a drawback ofthe zinc phosphate coating film, techniques utilizing a zircon coatingfilm have been established as a surface treatment method of automotivebodies, and thus an improvement of the adhesiveness of paint by adding aresin component, and providing a rust-preventive property through theaddition of a metal component have been attempted (see, Patent Documents3 to 5).

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 1998-204649

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. 2003-334490

Patent Document 3: Pamphlet of WO 2002/103080

Patent Document 4: Japanese Unexamined Patent Application PublicationNo. 2004-218070

Patent Document 5: Japanese Unexamined Patent Application PublicationNo. 2004-218075

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

According to a zircon coating film-based surface treatment technique,the amount of zircon coating film is likely to be lower on an aluminumcoated steel plate obtained by a hot stamping production method comparedto the amount of zircon coating film obtained on either an unprocessediron material or a galvanized steel plate, both of which are obtained bya hot stamping production method. Accordingly, conventional zirconcoating film-based surface treatment techniques cannot yield a coatedfilm having sufficient adhesiveness.

As previously described, a method of a chemical conversion treatmentwhich can ensure a sufficient amount of coating film, and cansimultaneously form coating films of the chemical conversion treatmentthat can achieve sufficient basis metal concealment and coated filmadhesiveness on any of a zinc-coated material, a cold-rolled steel platematerial, a galvanized steel plate material and an aluminum coated steelplate material has not been hitherto established. Therefore,establishment of such a method of the chemical conversion treatment isvery advantageous for automotive bodies, automobile parts and the likeconfigured with these materials.

The present invention was made in order to solve the aforementionedproblems, and an object of the invention is to provide a method of achemical conversion treatment which can ensure a sufficient amount ofthe coating film, and can simultaneously form a coating film of thechemical conversion treatment that can achieve sufficient basis metalconcealment and coated film adhesiveness on the surface of a zinccoating, a cold-rolled steel plate, a galvanized steel plate, analuminum coated steel plate and the like, and a member subjected to achemical conversion treatment obtained by this method of the chemicalconversion treatment.

Means for Solving the Problems

The present inventors undertook a detailed investigation in view of theaforementioned problems, and consequently discovered that the problemscan be solved by a chemical conversion treatment agent includingzirconium, fluorine, and an amino group-containing a silane couplingagent through specifying the ratio of these components. Accordingly, thepresent invention was accomplished. More specifically, the presentinvention provides the following.

In a first aspect of the present invention, a method of a chemicalconversion treatment for forming a chemical conversion coating filmincluding treating an object with a chemical conversion treatment agentis provided, wherein the object includes at least one aluminum coatedsteel plate, and at least one selected from the group consisting of acold-rolled steel plate, a galvanized steel plate, and an aluminumplate; the chemical conversion treatment agent contains zirconium,fluorine, and an amino group-containing silane coupling agent; thecontent of zirconium with respect to the metal content in the chemicalconversion treatment agent is no less than 100 ppm and no greater than700 ppm; and the molar ratio of fluorine to zirconium is no less than3.5 and no greater than 7.0.

In a second aspect of the present invention, the method of a chemicalconversion treatment according to the first aspect is provided, whereinthe content of the amino group-containing silane coupling agent in thechemical conversion treatment agent is no less than 50 ppm and nogreater than 500 ppm based on the solid content.

In a third aspect of the present invention, the method of a chemicalconversion treatment according to either the first or second aspect isprovided, wherein the pH of the chemical conversion treatment agent isno less than 2.6 and no greater than 4.5.

In a fourth aspect of the present invention, the method of a chemicalconversion treatment according to any one of the first to third aspectsis provided, wherein the chemical conversion treatment agent furthercontains at least one agent for imparting adhesiveness and corrosionresistance selected from the group consisting of a magnesium ion, a zincion, a calcium ion, an aluminum ion, a gallium ion, an indium ion, and acopper ion.

In a fifth aspect of the present invention, the method of a chemicalconversion treatment according to any one of the first to fourth aspectsis provided, wherein the object is a member for an automotive body, andan automotive body.

In a sixth aspect of the present invention, a member subjected to achemical conversion treatment is provided, including a conversioncoating film formed by the method of the chemical conversion treatmentaccording to any one of the first to fifth aspects.

EFFECTS OF THE INVENTION

According to the method of a chemical conversion treatment of thepresent invention, a method of a chemical conversion treatment which canensure a sufficient amount of the coating film, and can simultaneouslyform coating films of the chemical conversion treatment that can achievesufficient basis metal concealment and coated film adhesiveness on thesurface of not only a zinc coating, a cold-rolled steel plate, agalvanized steel plate, but also an aluminum coated steel plate and thelike, and a member subjected to a chemical conversion treatment obtainedby this method of the chemical conversion treatment can be provided.Thus, the variety of aluminum coated steel plates that can be used forautomotive bodies can be increased. Moreover, also on the edge part ofthe basis metal, the coating film can be readily formed, and thusprevent the generation of rust which has been a concern on parts wherethe basis iron metal is exposed due to cracking of the coating in thecourse of formation, scratches, and the like.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be explained.

Chemical Conversion Treatment Agent

The present invention is directed to a method of a chemical conversiontreatment for forming a chemical conversion coating film includingtreating an object with a chemical conversion treatment agent, whereinthe chemical conversion treatment agent contains zirconium, fluorine,and an amino group-containing silane coupling agent.

Zirconium Component

Zirconium included in the chemical conversion treatment agent is acomponent for forming the conversion coating film. Formation of theconversion coating film containing zirconium on the object enablesimprovement of the corrosion resistance and abrasion resistance of thebase material, and further increase the adhesiveness with the coatedfilm.

When the surface treatment of the object is conducted with the chemicalconversion treatment agent containing zirconium for use in the presentinvention, the solubilizing reaction of the metal that constitutes theobject results in production of a hydroxide or an oxide of zirconiumbecause a metal ion eluted into the chemical conversion treatment agentdraws fluorine of ZrF₆ ²⁻, and because the pH at the boundary iselevated. Accordingly, this hydroxide or oxide of zirconium isconsidered to be deposited on the surface of the object. Since thechemical conversion treatment agent used in the present invention is areactive chemical conversion treatment agent, it can also be used whenimmersing an object having a complicated shape. Furthermore, since theconversion coating film rigidly adhered to the object can be attained bya chemical reaction, washing with water can be also conducted after thetreatment.

The source of zirconium is not particularly limited, and examplesthereof include alkali metal fluorozirconates such as K₂ZrF₆,fluorozirconates such as (NH₄)₂ZrF₆, soluble fluorozirconates such asfluorozirconate acids such as H₂ZrF₆, zirconium fluoride, zirconiumoxide, zirconyl nitrate, and zirconium carbonate and the like.

Content of Zirconium

The content of zirconium included in the chemical conversion treatmentagent used in the present invention falls within a range of no less than100 ppm and no greater than 700 ppm expressed with respect to the metalcontent. When the content is less than 100 ppm, a sufficient amount ofthe coating film cannot be attained on the aluminum coated steel plate.In contrast, when the content exceeds 700 ppm, an economicaldisadvantage results because a much greater effect cannot be expected.Preferably, the content is no less than 150 ppm and no greater than 550ppm.

Fluorine Component

Fluorine included in the chemical conversion treatment agent used in thepresent invention plays a role as an etching agent of the object.Although the source of fluorine is not particularly limited, examplesthereof include fluorides such as hydrofluoric acid, ammonium fluoride,fluoborate, ammonium hydrogen fluoride, sodium fluoride, and sodiumhydrogen fluoride. Furthermore, a complex fluoride can be also used asthe source, and examples thereof include hexafluorosilicic acid salts,specifically, hydrofluosilicic acid, zinc hydrofluosilicicate, manganesehydrofluosilicate, magnesium hydrofluosilicate, nickelhydrofluosilicate, iron hydrofluosilicate, calcium hydrofluosilicate,and the like.

Content of Fluorine Component

With respect to the content of fluorine included in the chemicalconversion treatment agent used in the present invention, the molarratio of fluorine to zirconium falls within a range of no less than 3.5and no greater than 7.0. When the molar ratio of fluorine to zirconiumis lower than 3.5, precipitation may be result as the solution becomesunstable. In contrast, when the ratio is higher than 7.0 sufficientformation of the coating film is not achieved due to reduction in theetching force. The ratio is preferably, no less than 4.5 and no greaterthan 6.5, and more preferably no less than 5.0 and no greater than 6.0.

Amino Group-Containing Silane Coupling Agent

The amino group-containing silane coupling agent included in thechemical conversion treatment agent used in the present invention is acompound, which has at least one alkyl chain in the molecule, whereinthe at least one alkyl chain has at least one amino group, and whichincludes an alkoxy group or halogen (predominantly chlorine) as afunctional group or an element that binds to a dangling bond of silicon.Since the amino group-containing silane coupling agent acts on both ofthe conversion coating film and the coated film formed later,adhesiveness of both films can be improved.

Such an effect is speculated to be caused because silanol produced byhydrolysis of the alkoxy group is covalently adsorbed on the surface ofthe object, or on the surface of the zirconium coating film.

In addition, since the amino group-containing silane coupling agentincluded in the conversion coating film acts not only on the object butalso on the coated film formed later, it is believed to serve inimproving their adhesiveness with one another. In particular, the aminogroup-containing silane coupling agent can exhibit an effect to improvethe adhesiveness to the coated film formed with paint for cationelectrodeposition.

The amino group-containing silane coupling agent is not particularlylimited, and examples thereof include known silane coupling agents suchas N-2(aminoethyl)3-aminopropylmethyldimethoxysilane,N-2(aminoethyl)3-aminopropyltrimethoxysilane,N-2(aminoethyl)3-aminopropyltriethoxysilane,3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane,3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine,N-phenyl-3-aminopropyltrimethoxysilane,N,N-bis[3-(trimethoxysilyl)propyl]ethylenediamine, and3-aminopropyltrichlorosilane and the like. Moreover, KBM-602, KBM-603,KBE-603, KBM-903, KBE-9103, KBM-573 (manufactured by Shin-Etsu ChemicalCo., Ltd.), XS1003 (manufactured by Chisso Corporation) and the likewhich have been commercially available as amino group-containing silanecoupling agents can be also used intact. Among these,N-2(aminoethyl)3-aminopropyltriethoxysilane (APS-L),N-2(aminoethyl)3-aminopropyltrimethoxysilane (APS-L),3-aminopropyltriethoxysilane (APS-S), and 3-aminopropyltrimethoxysilaneare preferred.

Content of Amino Group-Containing Silane Coupling Agent

The content of the amino group-containing silane coupling agent includedin the chemical conversion treatment agent used in the present inventionfalls within a range of preferably no less than 50 ppm and no greaterthan 500 ppm based on the solid content. When the content is less than50 ppm, sufficient adhesiveness of the coated film may not be achieved.In contrast, when the content exceeds 500 ppm, an economicaldisadvantage results because a much greater effect cannot be expected.The content falls within a range of more preferably no less than 100 ppmand no greater than 300 ppm, and more preferably no less than 150 ppmand no greater than 250 ppm.

pH of Chemical Conversion Treatment Agent

The pH of the chemical conversion treatment agent used in the presentinvention is preferably no less than 2.6 and no greater than 4.5. Whenthe pH is lower than 2.6, sufficient formation of the coating film maynot be achieved due to excessive etching, or the resulting non-uniformcoating film may adversely affect the appearance of coated paint. Incontrast, when the pH is higher than 4.5, the etching may becomeinsufficient, thereby leading to failure in obtaining a favorablecoating film. The pH falls within a range of more preferably no lessthan 3.0 and no greater than 4.2, and still more preferably no less than3.2 and no greater than 4.0.

The pH of the chemical conversion treatment agent can be adjusted usingan acidic compound such as nitric acid or sulfuric acid, and a basiccompound such as sodium hydroxide, potassium hydroxide or ammonia.

Agent for Imparting Adhesiveness and Corrosion Resistance

It is preferred that the chemical conversion treatment agent used in thepresent invention further includes at least one agent for impartingadhesiveness and corrosion resistance selected from the group consistingof an iron ion, a magnesium ion, a zinc ion, a calcium ion, an aluminumion, a gallium ion, an indium ion, and a copper ion. In the presentinvention, the conversion coating film having more favorableadhesiveness and corrosion resistance can be obtained by including theagent for imparting adhesiveness and corrosion resistance.

Content of Agent for Imparting Adhesiveness and Corrosion Resistance

The content of the agent for imparting adhesiveness and corrosionresistance optionally added to the chemical conversion treatment agentused in the present invention preferably falls within a range of no lessthan 1 ppm and no greater than 5000 ppm. When the content is less than 1ppm a sufficient effect of imparting the adhesiveness and corrosionresistance cannot be achieved. In contrast, when the content exceeds5000 ppm an economical disadvantage results because any additionaleffect cannot be found, otherwise, the adhesiveness following paintingmay deteriorate. The content falls within a range of more preferably noless than 25 ppm and no greater than 1000 ppm.

Other Component

In the chemical conversion treatment agent used in the presentinvention, other optional component may be included in combination asneeded in addition to the aforementioned components. An exemplarycomponent that can be used is silica and the like. By adding such acomponent, an improvement in the corrosion resistance after painting isachieved.

Furthermore, it is preferred that the chemical conversion treatmentagent is an agent not substantially containing a phosphate ion. The term“not substantially containing a phosphate ion” means that a phosphateion is not included in an amount to exhibit an action as a component inthe chemical conversion treatment agent. By using the chemicalconversion treatment agent not substantially containing a phosphate ion,use of phosphorus which is responsible for environmental burden can beavoided, and generation of sludge such as iron phosphate, and zincphosphate can be prevented which may be produced in use of the zincphosphate-based treatment agent.

Method of Chemical Conversion Treatment

The method of the chemical conversion treatment of the present inventionis not particularly limited, and can be performed under a commontreatment condition by bringing the chemical conversion treatment agentinto contact with the surface of the object. Examples of the methodinclude a dipping method, a spraying method, a roll coating method andthe like.

Condition of Chemical Conversion Treatment

The treatment temperature in the chemical conversion treatment fallswithin a range of preferably no less than 20° C. and no greater than 70°C. More preferably, it falls within a range of no less than 30° C. andno greater than 50° C. When the temperature is less than 20° C.sufficient formation of the coating film may not be achieved, andadjustment of the temperature is necessary in summer. Also, when thetemperature is greater than 70° C. an economical disadvantage resultssince no additional effect is particularly exhibited. It is preferredthat the duration of the chemical conversion treatment fall within arange of no less than 5 sec and no greater than 1100 sec. Morepreferably, the duration falls within a range of no less than 30 sec andno greater than 120 sec. When the duration is less than 5 sec asufficient amount of the coating film cannot be achieved. When theduration is greater than 1100 sec an additional effect is not exhibitedwith a further increase in the amount of coated film.

In the method of the chemical conversion treatment of the presentinvention, surface conditioning treatment may not be conducted as inconventionally practiced treatment with a zinc phosphate-based chemicalconversion treatment agent. Thus, the chemical conversion treatment ofthe object can be conducted with fewer steps.

Object

Examples of the object which may be used in the method of the chemicalconversion treatment of the present invention include iron-based basematerials, aluminum-based base materials, and zinc-based base materialsand the like. The iron, aluminum, and zinc-based base materials meaniron-based base material constituted with iron and/or an alloy thereof,aluminum base materials constituted with aluminum and/or an alloythereof, and zinc-based base materials constituted with zinc and/or analloy thereof.

Particularly, in the present invention, a sufficient amount of thezircon coating film can be achieved on the aluminum coated steel platesafter the hot stamping, which had conventionally involved problems, andsufficient paint adhesiveness can be achieved even on an aluminum coatedsteel plate.

Moreover, the method of the chemical conversion treatment of the presentinvention can be simultaneously applied to an object constituted withmultiple metal base materials among an iron-based base material, analuminum-based base material, and a zinc-based base material. Theautomotive bodies, the automobile parts, and the like are configuredwith items constituted with various metal materials such as iron, zinc,aluminum and the like. Therefore, there may be the case in which thesurface treatment therefor must be conducted on all materials by asingle treatment. However, according to the method of the chemicalconversion treatment of the present invention, the chemical conversiontreatment can be achieved on all the materials without problem in asingle operation.

The iron-based base materials used as the object of the presentinvention are not particularly limited, and examples thereof includecold-rolled steel plates and hot-rolled steel plates. The aluminum-basedbase materials are also not particularly limited, and examples thereofinclude 5000 series aluminum alloy, 6000 series aluminum alloy, andaluminum-coated steel plates treated by aluminum-based electroplating,hot dipping, or vapor deposition plating. Furthermore, zinc-based basematerials are also not particularly limited, and examples thereofinclude zinc or zinc-based alloy coated steel plates treated byzinc-based electroplating, hot dipping, or vapor deposition plating,such as galvanized steel plate, zinc-nickel coated steel plate,zinc-iron coated steel plate, zinc-chromium coated steel plate,zinc-aluminum coated steel plate, zinc-titanium coated steel plate,zinc-magnesium coated steel plate, and zinc-manganese coated steelplate. In the present invention, iron, aluminum and zinc-based basematerials can be simultaneously subjected to the chemical conversiontreatment.

Average Amount of Coating Film of Conversion Coating Film

Average amount of the coating film of the conversion coating filmobtained by the method of the chemical conversion treatment of thepresent invention preferably falls within a range of no less than 0.1mg/m² and no greater than 500 mg/m² based on the total amount of themetal included in the chemical conversion treatment agent. An averageamount of less than 0.1 mg/m² is not preferred because a uniformconversion coating film cannot be obtained, and hence favorableadhesiveness may not be achieved. In contrast, an average amountexceeding 500 mg/m² is economically disadvantageous since any greatereffect cannot be exhibited. More preferably, the average amount fallswithin a range of no less than 5 mg/m² and no greater than 150 mg/m².

In the method of the chemical conversion treatment of the presentinvention, a sufficient amount of the zircon coating film can beachieved also on the aluminum coated steel plates after the hotstamping, which had conventionally involved problems, and sufficientpaint adhesiveness can be achieved even on the aluminum coated steelplates. Thus, also in the case in which the chemical conversiontreatment is simultaneously applied to the object constituted withmultiple metal base materials including an aluminum coated steel plate,sufficient paint adhesiveness can be achieved. According to the methodof the chemical conversion treatment of the present invention, theaverage amount of the conversion coating film of no less than 10 mg/m²can be achieved also on the aluminum coated steel plates.

Coated Film Formed Later

As the coated film formed on the conversion coating film after theformation of the conversion coating film by the method of the chemicalconversion treatment of the present invention, coated films formed witha conventionally known paint such as a cation electrodeposition paint, asolvent paint, an aqueous paint, a powder paint or the like may beexemplified. Examples of the cation electrodeposition paint includeconventionally known cation electrodeposition paints such as aminatedepoxy resins, aminated acrylic resins, sulfonium epoxy resins and thelike. Among these, because adhesiveness of the conversion coating filmwith the electrodeposition coated film can be further improved due tothe action of the amino group-containing silane coupling agent includedin the chemical conversion treatment agent, cation electrodepositionpaints including a resin that has a functional group exhibitingreactivity or compatibility with the amino group are preferred.

Pretreatment of Object

It is preferred that the object of the present invention is subjected toa degreasing treatment followed by a water washing treatment beforeconducting the aforementioned chemical conversion treatment. Thedegreasing treatment is conducted in order to remove oil and stainsadhered to the surface of the object. In usual cases, immersiontreatment is conducted for several minutes at a temperature from 30° C.to 55° C. using a degreasing agent such as a phosphate-free andnitrogen-free degreasing detergent. If desired, preliminary degreasingtreatment may be conducted before the degreasing treatment. Furthermore,a water washing treatment following the degreasing treatment isconducted for washing away the degreasing agent, at least once by aspray treatment with a large amount of washing water.

Post-Treatment of Object

The member subjected to the chemical conversion treatment having theconversion coating film formed by the method of the chemical conversiontreatment of the present invention is preferably subjected to waterwashing treatment before the formation of the coated film to beconducted later. The water washing treatment following the chemicalconversion treatment is conducted at least once so as not to adverselyaffect adhesiveness, corrosion resistance and the like after completingthe following various types of painting. In this case, it is suitable toconduct the final water washing with pure water. The water washingtreatment following the chemical conversion treatment may be eitherspray water washing or immersion water washing, and combination of theseis also acceptable for the water washing. After conducting the waterwashing treatment following the chemical conversion treatment, theobject is dried according to a known method as needed, and thereafter,the coated film is formed with various types of painting.

EXAMPLES

Next, the present invention will be explained more specifically by wayof Examples and Comparative Examples, but the present invention is notlimited only to these Examples. The amount to be blended is representedby parts by weight unless specifically stated otherwise.

Example 1

A commercially available cold-rolled steel plate (SPCC-SD, manufacturedby Nippon Testpanel Co., Ltd., 70 mm×150 mm×0.8 mm), a high-tensilesteel plate (JSC780T, manufactured by Nippon Steel Corporation, 70mm×150 mm×0.8 mm), and an aluminum coated steel plate (USIBOR1500P,manufactured by ARCELOR S. A., 70 mm×150 mm×2.3 mm) were provided as theobject.

Pretreatment of Object Before Chemical Conversion Treatment DegreasingTreatment

Using 1.6% by weight of EC90 (degreasing agent, manufactured by NipponPaint Co., Ltd.), an immersion treatment was conducted at 42° C. for 2min.

Water Washing Treatment

After conducting the degreasing treatment, the object was subjected toimmersion washing with a water washing bath. Thereafter, spray washingwas carried out with tap water for about 30 sec.

Chemical Conversion Treatment

Using zirconyl nitrate (manufactured by Nippon Light Metal Co., Ltd.) asthe zirconium source, and KBE-903 (APS-S) (aminopropyltriethoxysilane:effective concentration: 100%, manufactured by Shin-Etsu Chemical Co.,Ltd.) as the amino group-containing silane coupling agent, the chemicalconversion treatment agent having a zirconium content of 500 ppm, afluorine content of 416 ppm (molar ratio=416×91.2/500×19.0=4.0), and theamino group-containing silane coupling agent content of 100 ppm based onthe solid content was prepared including 100 ppm of a magnesium ion, and500 ppm of a zinc ion, as the agent for imparting adhesiveness andcorrosion resistance. Furthermore, the pH was adjusted to give 2.8 witha 10% aqueous sodium hydroxide solution. The temperature of the chemicalconversion treatment agent was adjusted to 40° C., and thereafter, theobject was subjected to the immersion treatment for 60 sec.

Measurement of Amount of Coating Film

The amount of the coating film following the chemical conversiontreatment was determined on each steel plate. With respect to the amountof the coating film, the amount of Zr (mg/m²) and the amount of Si(mg/m²) included in the coating film of the chemical conversiontreatment were measured using a fluorescent X-ray analyzer XRF-1700 (anapparatus for fluorescent X-ray analysis, manufactured by ShimadzuCorporation). The results are shown in Table 1.

Water Washing Treatment Following the Chemical Conversion Treatment

On each steel plate subjected to the chemical conversion treatment aspray treatment with tap water was conducted for 30 sec. Subsequently,the spray treatment was conducted with ion exchanged water for 30 sec.

Electrodeposition Painting

Electrodeposition painting was carried out on each of the steel plateswhile in a wet state resulting from the water washing treatment thatfollowed the chemical conversion treatment. The electrodepositionpainting was performed using PN150 (cation electrodeposition paint,manufactured by Nippon Paint Co., Ltd.) so as to give a dry filmthickness of 20 μm. After forming the coated film by electrodepositionpainting, each steel plate was washed with water. Then, baking wasconducted at 170° C. for 20 min to obtain a test plate.

Secondary Adhesiveness Test (SDT)

Thus resulting test plate was incised to provide two parallel cut linesthat run longitudinally, with the depth to reach to the basis metal.Then, immersion in a 5% aqueous NaCl solution was carried out at 55° C.for 240 hrs. Thereafter, a tape was attached at the location of the cutand then peeled, and the stripped state of the paint was observed.Depending on the size of the maximum stripped width, the followingevaluation was made. The results are shown in Table 1.

A: Less than 1 mm

B: 1 mm to 2 mm

C: 2 mm to 3 mm

D: Greater than 3 mm

Complex Cycle Test (CCT)

Thus resulting test plate was incised to provide parallel cuts that runlongitudinally, with the depth to reach to the basis metal. Then, a 5%aqueous NaCl solution was continuously sprayed for 2 hrs in a salt spraytest unit maintained at 35° C. Then, the test plate was dried at 60° C.and a humidity of 20 to 30% for 4 hrs, followed by keeping under a humidcondition at 50° C. and a humidity of 95% or higher for 2 hrs. Such asequence of procedures was defined as one cycle, and 100 cycles werecarried out. After carrying out 100 cycles, the width bulged from thecut part was measured. Depending on the size of the maximum bulgedwidth, the following evaluation was made. The results are shown in Table1.

A: Less than 3 mm

B: 3 mm to 4 mm

C: 4 mm to 5 mm

D: Greater than 5 mm

Example 2

A similar operation to Example 1 was performed except that the fluorinecontent was 570 ppm (molar ratio=570×91.2/500×19.0=5.5); KBM-603 (APS-L)(N-(2-aminoethyl)-3-aminopropyltriethoxysilane, effective concentration:100%, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as theamino group-containing silane coupling agent at 100 ppm based on thesolid content; and the pH was adjusted to 3.5 to obtain a test plate.The evaluation results of the resulting test plate are shown in Table 1.

Example 3

A similar operation to Example 1 was performed except that the fluorinecontent was 574 ppm (molar ratio=574×91.2/500×19.0=5.5); KBM-603 (APS-L)(N-(2-aminoethyl)-3-aminopropyltriethoxysilane, effective concentration:100%, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as theamino group-containing silane coupling agent at 200 ppm based on thesolid content; and the pH was adjusted to 3.5 to obtain a test plate.The evaluation results of the resulting test plate are shown in Table 1.

Example 4

A similar operation to Example 1 was performed except that the zirconiumcontent was 200 ppm, and the fluorine content was 210 ppm (molarratio=210×91.2/200×19.0=5.0); and the pH was adjusted to 3.5 to obtain atest plate. The evaluation results of the resulting test plate are shownin Table 1.

Example 5

A similar operation to Example 1 was performed except that the zirconiumcontent was 200 ppm, and the fluorine content was 210 ppm (molarratio=210×91.2/200×19.0=5.0); the amino group-containing silane couplingagent was not used; and the pH was adjusted to 3.5 to obtain a testplate. The evaluation results of the resulting test plate are shown inTable 1.

Example 6

A similar operation to Example 1 was performed except that the fluorinecontent was 626 ppm (molar ratio=626×91.2/500×19.0=6.0); KBM-603 (APS-L)(N-(2-aminoethyl)-3-aminopropyltriethoxysilane, effective concentration:100%, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as theamino group-containing silane coupling agent at 250 ppm based on thesolid content; a zinc ion was used at 500 ppm as the agent for impartingadhesiveness and corrosion resistance; and the pH was adjusted to 3.5 toobtain a test plate. The evaluation results of the resulting test plateare shown in Table 1.

Comparative Example 1

A similar operation to Example 1 was performed except that the chemicalconversion treatment was changed to a treatment with zinc phosphate asdescribed below to obtain a test plate. The evaluation results of theresulting test plate are shown in Table 1.

Treatment with Zinc Phosphate

Surface conditioning of each object subjected to the degreasingtreatment and water washing treatment was carried out using 0.3% GL1(surface conditioning agent, manufactured by Nippon Paint Co., Ltd.) byimmersion at room temperature for 30 sec. Thereafter, Surfdyne SD-6800(zinc phosphate-based chemical conversion treatment agent, manufacturedby Nippon Paint Co., Ltd.) was used to conduct the immersion treatmentat 42° C. for 2 min.

Comparative Example 2

A similar operation to Example 1 was performed except that the zirconiumcontent was 100 ppm, and the fluorine content was 250 ppm (molarratio=250×91.2/100×19.0=12.0); and the pH was adjusted to 3.5 to obtaina test plate. The evaluation results are shown in Table 1.

Comparative Example 3

A similar operation to Example 2 was performed except that the fluorinecontent was 940 ppm (molar ratio=940×91.2/500×19.0=9.0); KBM-603 (APS-L)(N-(2-aminoethyl)-3-aminopropyltriethoxysilane, effective concentration:100%, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as theamino group-containing silane coupling agent at 250 ppm based on thesolid content; the agent for imparting adhesiveness and corrosionresistance was not used; and the pH was adjusted to 3.5 to obtain a testplate. The evaluation results are shown in Table 1.

TABLE 1 Composition of Chemical Conversion Bath CCT Zr F APS-S APS-L MgZn Base 60 SDT Examples ppm ppm ppm ppm ppm ppm pH Material Cycles 240 hExample 500 416 100 — 100 500 2.8 SPC A A 1 780T A A Al/Fe A A Example500 570 — 100 100 500 3.5 SPC A A 2 780T A A Al/Fe A A Example 500 574 —200 100 500 3.5 SPC A A 3 780T A A Al/Fe A A Example 200 210 100 — 100500 3.5 SPC A A 4 780T A A Al/Fe A A Example 200 210 — — 100 500 3.5 SPCA A 5 780T A A Al/Fe A A Example 500 626 — 250 — 500 3.5 SPC A A 6 780TA A Al/Fe A A Comparative Treatment with Zinc Phosphate 3.5 SPC A BExample 780T A B 1 Al/Fe A C Comparative 100 250 100 — 100 500 3.5 SPC AB Example 780T C B 2 Al/Fe A C Comparative 500 940 — 250 — — 3.5 SPC A BExample 780T C B 3 Al/Fe A C APS-S: NH₂(CH₂)₃Si(OC₂H₅)₃ APS-L:NH₂(CH₂)₂NH(CH₂)₃Si(OC₂H₅)₃

INDUSTRIAL APPLICABILITY

The member subjected to the chemical conversion treatment obtainedaccording to the present invention can ensure a sufficient amount of thecoating film also on the aluminum coated steel plate, and a sufficientamount of the coating film of the chemical conversion treatment can besimultaneously formed on various types of objects. In addition,sufficient corrosion resistance can be achieved. Therefore, it ispreferably used in a field of outside plates of vehicles such asautomotive bodies, bodies of two-wheeled vehicles before painting,various types of parts, outer surfaces of vessels, coil coatings, andthe like, which will subsequently be subjected to painting.

1-6. (canceled)
 7. A method of a chemical conversion treatment forforming a chemical conversion coating film comprising treating an objectwith a chemical conversion treatment agent, wherein the object includesat least one aluminum coated steel plate, and at least one selected fromthe group consisting of a cold-rolled steel plate, a galvanized steelplate, and an aluminum plate; the chemical conversion treatment agentcomprises zirconium, fluorine, and an amino group-containing silanecoupling agent; the content of zirconium with respect to metal contentin the chemical conversion treatment agent is no less than 100 ppm andno greater than 700 ppm; and the molar ratio of fluorine to zirconium isno less than 3.5 and no greater than 7.0.
 8. The method of a chemicalconversion treatment according to claim 7 wherein the content of theamino group-containing silane coupling agent in the chemical conversiontreatment agent is no less than 50 ppm and no greater than 500 ppm withrespect to the solid content.
 9. The method of a chemical conversiontreatment according to claim 7 wherein the pH of the chemical conversiontreatment agent is no less than 2.6 and no greater than 4.5.
 10. Themethod of a chemical conversion treatment according to claim 8 whereinthe pH of the chemical conversion treatment agent is no less than 2.6and no greater than 4.5.
 11. The method of a chemical conversiontreatment according to claim 7 wherein the chemical conversion treatmentagent further comprises at least one agent for imparting adhesivenessand corrosion resistance selected from the group consisting of amagnesium ion, a zinc ion, a calcium ion, an aluminum ion, a galliumion, an indium ion, and a copper ion.
 12. The method of a chemicalconversion treatment according to claim 7 wherein the object is a memberfor an automotive body, and an automotive body.
 13. A member subjectedto a chemical conversion treatment comprising a conversion coating filmformed by the method of the chemical conversion treatment according toclaim 7.